1. Field of the Invention
The disclosures discussed herein relate to a driving device of a liquid-jet head to eject liquid drops from nozzles of the liquid-jet head, a liquid-jet device having such a driving device and a method for driving a liquid-jet head.
2. Description of the Related Art
There are various types of technologies for causing nozzles provided in a liquid-jet head to eject liquid drops.
For example, a piezo-type liquid-jet head is configured to eject liquid drops by utilizing a piezoelectric device to deform a vibrating plate constituting a wall surface of a liquid channel to change the volume of the liquid channel. Further, a thermal-type liquid-jet head is configured to eject liquid drops by utilizing a heat element to heat liquid inside a liquid channel to generate air bubbles such that the liquid drops are ejected by the pressure generated by the air bubbles. In addition, a electrostatic-type liquid-jet head is configured to eject liquid drops by utilizing electrostatic force generated between a vibrating plate and an electrode to deform the vibrating plate constituting a wall surface of a liquid channel to change the volume of the liquid channel.
Mechanical structures of the liquid-jet heads of these types may be easily simplified and downsized. Accordingly, the liquid-jet heads may be fabricated by utilizing an integrated circuit (IC) technology or a microprocessing technology markedly advanced in the recent semiconductor field, which may provide advantages for implementing high-density packaging while reducing the fabrication cost.
Further, since the liquid-jet heads of the above types electrically control ejection of liquid drops, various sizes of the liquid drops may be precisely controlled. Accordingly, it is advantageous for the liquid-jet heads of the aforementioned types to be incorporated into recording devices configured to eject microscopic liquid drops to form high definition images.
The liquid-jet device generally includes a liquid-jet head having a series of liquid drop channels including a pressure chamber containing liquid, plural nozzle arrays communicating with the pressure chamber and piezoelectric devices corresponding to the nozzles, and a driving signal generator circuit configured to generate driving signals to be applied to the piezoelectric devices. In the aforementioned configuration, the liquid-jet device is capable of ejecting liquid drops from the nozzles by applying driving signals generated from the driving signal generator circuit to the piezoelectric devices so as to change the pressure inside the pressure chamber.
Examples of wiring member to transmit the driving signals generated from the driving signal generator circuit include a flexible flat cable (hereinafter simply called “FFC”) or a flexible printed circuit board (hereinafter simply called “FPC”).
The wiring member generally includes an inductance component L, other than a resistance component R, that with a change in the current produced on induced electromotive force. The inductance component L has a property of changing the magnitude of the inductance component L based on the length of wire.
The resistance component R of the wiring member is extremely small. Hence, even if the length of wire is increased, the transmission of the driving signals will not be interfered with. However, the inductance component L changes with the length of wire or the diameter of a path, which generates the counter electromotive force ΔE (=L×(di/dt)) that represents a product of the inductance component L and the current change rate per unit time (di/dt).
When the inductance component L becomes large due to an increase in the length of the wiring member, the counter electromotive force ΔE may become too large to be ignored as noise, which may become a cause of driving waveform distortion. The noise caused by the inductance component L may appear as overshoot or undershoot in the driving waveform.
If the amount of the overshoot or undershoot occurring in the driving waveform is constant, the driving waveform and the driving signal generator circuit may be prepared based on anticipation that such driving waveform distortion will occur.
However, the magnitude of overshoot or undershoot changes with the amount of current passing through the wiring member, which indicates that the magnitude of overshoot or undershoot changes with the number of nozzles that are driven in the liquid-jet head.
That is, if the number of nozzles is small, the driving waveform distortion may be small, and if the number of nozzles is large, the driving waveform distortion may be large. Hence, the driving waveform changes with the number of driven nozzles, which may cause a change in liquid-jet properties.
Japanese Laid-open Patent Publication No. 2007-203493 (hereinafter referred to as “Patent Document 1”) discloses a technology for stabilizing ink drop ejection properties. In this technology, the inkjet printer includes plural capacitive loads to be connected to/disconnected from a supply wire of a drive pulse in parallel. The connection/disconnection conditions of the capacitive loads to the supply wire of the drive pulse are set based on either the number of nozzles driven for ejecting ink droplets or piezoelectric actuators for driving the nozzles. This makes total electrostatic capacitance of the capacitive loads to be connected to the supply wire of the drive pulse to be a constant value. As a result, the ink drop ejection properties may be stabilized.